When you say stage... are you talking theatre or band? I find 2.8 near the limit in small clubs. And in dim light you risk motion blur
by not getting fast enough shutter. Are you in a situation where you must just use the stage lighting and no flash?
I love my 28-75 it is my workhorse for family shots and for club stuff... the 28-75 range is perfect for both things.
But 2.8 and a poorly lit stage is a tough combo...
Here are a couple indoor club shots... at 2.8
K100d ISO 3200 with Tammy 28-75 at 50mm
This is K100d ISO 1600 at 75mm f2.8